WEDNESDAY, May 25 (HealthDay News) -- Older adults who say they've had a life-changing religious experience are more likely to have a greater decrease in size of the hippocampus, the part of the brain critical to learning and memory, new research finds.

According to the study, people who said they were a "born-again" Protestant or Catholic, or conversely, those who had no religious affiliation, had more hippocampal shrinkage (or "atrophy") compared to people who identified themselves as Protestants, but not born-again.

As people age, a certain amount of brain atrophy is expected. Shrinkage of the hippocampus is also associated with depression, dementia and Alzheimer's disease.

In the study, researchers asked 268 people aged 58 to 84 about their religious affiliation, spiritual practices and life-changing religious experiences. Over the course of two to eight years, changes to the hippocampus were monitored using MRI scans.

The researchers suggested that stress over holding religious beliefs that fall outside of the mainstream may help explain the findings.

"One interpretation of our finding -- that members of majority religious groups seem to have less atrophy compared with minority religious groups -- is that when you feel your beliefs and values are somewhat at odds with those of society as a whole, it may contribute to long-term stress that could have implications for the brain," Amy Owen, lead author of the study and a research associate at Duke University Medical Center, said in a Duke news release.

The study authors also suggested that life-changing religious experiences could challenge a person's established religious beliefs, triggering stress.

"Other studies have led us to think that whether a new experience you consider spiritual is interpreted as comforting or stressful may depend on whether or not it fits in with your existing religious beliefs and those of the people around you," David Hayward, research associate at Duke University Medical Center, added. "Especially for older adults, these unexpected new experiences may lead to doubts about long-held religious beliefs, or to disagreements with friends and family."

The researchers noted other factors related to hippocampal atrophy, such as age, depression or brain size, as well as other religious factors such as prayer or meditation, could not explain the study's findings.

More information

The U.S. National Institute of Neurological Disorders and Stroke provides details on brain atrophy.